Creating Empathy Maps is useful for synthesizing research data in order to better understand the users. Empathy Maps are great for creating Personas, identifying users with different mindsets.
Jakob Nielsen's 10 general principles for interaction design. They are called "heuristics" because they are broad rules of thumb and not specific usability guidelines.
Usability
10 Usability Heuristics for User Interface Design
Knowledge
How to Improve Your Design Team’s Productivity — The Startup